This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
Various abbreviations that appear in the specification and/or in the drawing figures are defined as follows:
3GPP third generation partnership project
ACK acknowledge
AN ACK/NACK
CM cubic metric
CP cyclic prefix
CQI channel quality indicator
DAI downlink activity indicator
DFT discrete Fourier transform
DL downlink (eNB towards UE)
DTX discontinuous transmission
eNB EUTRAN Node B (evolved Node B)
EPC evolved packet core
EUTRAN evolved UTRAN (LTE)
FDD frequency division duplex
FDMA frequency division multiple access
HARQ hybrid automatic repeat request
LTE long term evolution
MAC medium access control
MIMO multiple input multiple output
MM mobility management
MME mobility management entity
MSM multi-sequence modulation
NACK not (negative) acknowledge
Node B base station
O&M operations and maintenance
OC orthogonal cover
OCC orthogonal cover code
OFDMA orthogonal frequency division multiple access
PDCP packet data convergence protocol
PHY physical
PRB physical resource block (180 kHz)
PUCCH physical uplink control channel
PUSCH physical uplink shared channel
QPSK quadrature phase shift keying
RB resource block
RLC radio link control
RRC radio resource control
RRM radio resource management
RS reference signal
S synchronous
SC-FDMA single carrier, frequency division multiple access
SF spreading factor
S-GW serving gateway
SIMO single input multiple output
SR scheduling request
TDD time division duplex
TTI transmission time interval
UE user equipment
UL uplink (UE towards eNB)
UTRAN universal terrestrial radio access network
ZAC zero auto-correlation code
The specification of a communication system known as evolved UTRAN (E-UTRAN, also referred to as UTRAN-LTE or as E-UTRA) is nearing completion within 3GPP. In this system the DL access technique will be OFDMA and the UL access technique will be SC-FDMA.
One specification of interest is 3GPP TS 36.300, V8.4.0 (2008-03), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Access Network (E-UTRAN); Overall description; Stage 2 (Release 8). One section of particular relevance to the ensuing discussion is Section 5.2, Uplink Transmission Scheme.
FIG. 5 reproduces FIG. 4 of 3GPP TS 36.300, and shows the overall architecture of the E-UTRAN system. The E-UTRAN system includes eNBs, providing the E-UTRA user plane (PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towards the UE. The eNBs are interconnected with each other by means of an X2 interface. The eNBs are also connected by means of an S1 interface to an EPC, more specifically to a MME (Mobility Management Entity) by means of a S1-MME interface and to a Serving Gateway (S-GW) by means of a S1-U interface. The S1 interface supports a many-to-many relation between MMES/Serving Gateways and eNBs.
The eNB hosts the following functions:                functions for Radio Resource Management: Radio Bearer Control, Radio Admission Control, Connection Mobility Control, Dynamic allocation of resources to UEs in both uplink and downlink (scheduling);        IP header compression and encryption of user data stream;        selection of a MME at UE attachment;        routing of User Plane data towards Serving Gateway;        scheduling and transmission of paging messages (originated from the MME);        scheduling and transmission of broadcast information (originated from the MME or O&M); and        measurement and measurement reporting configuration for mobility and scheduling.        
Of particular interest herein are the Layer 1 (PHY) specifications, such as those found in 3GPP TS 36.211 V8.2.0 (2008-03), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation (Release 8). More specifically, of particular relevance herein is the resource allocation for dynamic ACK/NACK resources (PUCCH Format 1a/1b) in the TDD mode of the LTE system.
There are certain differences between the LTE TDD and FDD modes regarding control signaling. In the FDD mode each DL sub-frame has a dedicated UL sub-frame to be used to transmit DL related L1/L2 control signals, such as ACK/NACK. However, in the TDD mode a single UL sub-frame is required to support the signaling of L1/L2 control signals from multiple DL sub-frames. The number of DL sub-frames associated with a single UL sub-frame depends on the DL-UL ratio, which is configured by broadcast system information.
Two different approaches have been discussed in 3GPP regarding the ACK/NACK signaling in TDD mode. A first approach can be referred to as ACK/NACK bundling (bundled-AN), where ACK/NACK feedback related to multiple DL sub-frames is compressed into a single ACK/NACK feedback transmitted via a single ACK/NACK resource. A second approach can be referred to as multi-ACK/NACK (multi-AN), where each DL sub-frame is considered as a separate HARQ process, and where a separate ACK/NACK feedback is transmitted for each (granted) DL sub-frame.
The 3GPP specification effort related to the ACK/NACK bundling approach is almost complete, while the multi-ACK/NACK approach is currently an open item in the LTE Rel. 8 specifications.
Due to the implicit mapping, the ACK/NACK channel on the PUCCH is required to be pre-configured by broadcast higher layer signaling. This pre-configuration is referred to as ACK/NACK channelization. There is an existing channelization approach for the case where the given RB is used exclusively for a single ACK/NACK channel. Furthermore, there is a mechanism to support mixed allocation of ACK/NACKs (PUCCH Format 1/1a/1b) and periodic CQIs (PUCCH Format 2/2a/2b) in a single PUCCH PRB. All of these channelization arrangements are described in Section 5.4.1 of 3GPP TS 36.211. However, at present there is no agreed upon channelization solution for the multi-ACK/NACK approach.
Proposals that have been discussed in 3GPP to arrange the multi-ACK/NACK transmission in the PUCCH include the use of PUCCH Format 2 and block level spreading on top of the DFT-S-OFDMA transmission.
One problem inherent in these proposals is that the multiplexing capacity is basically only a maximum 6 UEs/RB. Another issue is that these proposals are not truly compatible with the existing PUCCH Format 1/1a/1b channelization. Note that PUCCH Format 1 channelization is used in the case of the bundled ACK/NACK approach.
It can be noted that multi-sequence modulation (MSM) has been previously proposed for LTE Rel. 8 FDD use. Reference in this regard can be made to R1-080938, 3GPP TSG RAN WG1 Meeting #52, Sorrento, Italy, Feb. 11-15, 2008, “Comparison of single-sequence and multi-sequence modulation with existing DM RS sequence set”, Nokia Siemens Networks, Nokia. Reference can also be made to R1-073658, 3GPP TSG RAN WG1 Meeting #50, Athens, Greece, Aug. 20-24, 2007, “Increasing the size of the CQI by means of enhanced sequence modulation”, Nokia Siemens Networks, Nokia. One goal of these proposals is to increase the control payload of the PUCCH Format 2